1. Field of the Invention
The present invention relates generally to link layer protocols, and more particularly to a data link protocol for third generation (3G) wireless systems for direct support of network layer protocol data services, i.e. the Internet Protocol (IP).
2. Description of the Related Art
Layered architecture is a form of hierarchical modularity used in data network design. All major emerging communication network technologies rest on the layers of the International Organization for Standardization (ISO/OSI) model, illustrated in FIG. 1A. A layer performs a category of functions or services. The OSI model defines a Physical Layer (Layer 1) which specifies the standards for the transmission medium, a Data Link Layer (Layer 2), a Network Layer (Layer 3), a Transport Layer (Layer 4) and Application Layers (Layers 5 to 7).
Data link layer protocols are used to mitigate the effects of impairments introduced by the physical transmission medium. A Radio Link Protocol (RLP) is designed for the wireless system to deal specifically with the types of impairments found on the radio link and comprises mechanisms to deal with errors on the communications link, delays encountered in transmitting information, lost information, bandwidth conservation, and contention resolution.
The third layer is the Network Layer which implements routing and flow control for the network.
The fourth layer, Transport Layer, provides reliable and transparent transfer of data between end points. It provides end-to-end error recovery and flow control. For the Internet based protocol model, the Transport Control Protocol (TCP) mainly corresponds to the Transport Layer of the OSI model.
FIG. 2 shows the OSI Data Link Protocol architecture layer proposed for a 3G wireless network, and more particularly for a code division multiple access, i.e. xe2x80x9cThe cdma2000 RTT Candidate Submissionxe2x80x9d, Jun. 2, 1998 (TIA TR-45.5) network. At the most basic level, the TIA TR-45.5 layer structure provides protocols and services that correspond to the bottom two layers Layer 1xe2x80x94the physical layer 20 and Layer 2xe2x80x94the Data Link Layer (DLC) 30 of the OSI architecture, according to the general structure specified by the xe2x80x9cInternational Mobile Telecommunications-2000xe2x80x9d (ITU IMT-2000).
Layer-1, i.e. the Physical Layer 20 is responsible for coding and modulation of data transmitted over the air, and is not shown in FIG. 2 for simplification.
Layer-2, i.e. the Link Layer 30 is subdivided into the Link Access Control (LAC) sublayer 32 and the Medium Access Control (MAC) sublayer 31. The separation in MAC and LAC sublayers is motivated by the need to support a wide range of upper layer services, and the requirement to provide for high efficiency and low latency data services over a wide performance range (from 1.2 Kbps to greater than 2 Mbps). Other motivators are the need for supporting high QoS delivery of circuit and packet data services, such as limitations on acceptable delays and/or data BER (bit error rate), and the growing demand for advanced multimedia services each service having a different QoS requirements.
LAC sublayer 32 is required to provide a reliable, in-sequence delivery transmission control function over a point-to-point radio transmission link 42.
The MAC sublayer 31 includes procedures 35 for controlling the access of data services (packet and circuit) to the Physical Layer 20, including the contention control between multiple services from a single user, as well as between users in the wireless system. The MAC sublayer 31 services include a best effort delivery RLP 33, which provides for a reasonably reliable transmission over the radio link layer, using a Radio Link Protocol (RLP) that provides a xe2x80x9cbest effortxe2x80x9d level of reliability. Multiplexing and QoS (quality of service) control 34 is responsible for enforcement of negotiated QoS levels by mediating conflicting requests from competing services and the appropriate prioritization of access requests. MAC Control States, block 35, and QoS control side of block 34, are again specific to the TIA TR-45.5 system.
The MAC is divided into two sections namely a physical layer independent convergence function (PLICF) section, and a physical layer dependent convergence function (PLDCF) section. A state machine running in the PLICF section regulates the delivery of the LAC PDU""s to the Radio Link Protocol (RLP) which is mainly located in the PLDCF. The PLDCF also contains a multiplexing and QoS control module which multiplexes the RLP frames onto different physical channels based on their QoS requirements. Again, the wireless data link layer may be viewed as an interface between the upper layers and the wireless Physical Layer.
As illustrated in FIG. 2 in the Transport Layer 50 are the Transport Control Protocol (TCP) 51 and the User Datagram Protocol (UDP) 52. A Hyper Text Transport Protocol (HTTP), a Real-time Transport Protocol (RTP), or other protocols may also be present.
The upper layers 5 to 7, denoted in this figure with 60, include the session, presentation and application layers for packet data applications 61, voice services 62, simple circuit data applications (e.g. asynchronous fax) 63, and simultaneous voice and packet data service. Voice services 62 may utilize directly the services provided by the TIA TR-45.5 LAC services. Signaling services 70 are illustrated over layers 40, 50 and 60, to indicate that the signaling information is exchanged between all layers 3-7 and the DLC layer.
Current wireless networks use layer 2-4 protocols designed specifically for the wired networks. However, there are some major differences between the wireless and wired environment, resulting in important differences in the way these networks operate.
In a wired network the bit error rates are typically on the order of 10xe2x88x929 or better, and errors and packet loss have a tendency to be random. Therefore, the wired transmission medium could be considered essentially error-free and the TCP data packets are lost mainly due to congestion in the intervening routers. Moreover, in a wired system the transmission channel has a constant bandwidth and is symmetrical, which means the characteristics of the channel in one direction can be deduced by looking at the characteristics of the channel in the other direction. Therefore, it is often easiest to use a common link control protocol and to solve congestion problems by adding bandwidth.
On the other hand, in a wireless environment, most of these assumptions are no longer valid. The wireless channel is characterized by a high bit error rate. The errors occur in bursts that can affect a number of successive packets. Due to fading, the low transmission power available to the Mobile Station (MS) and the effects of interference, the radio link is not symmetrical and the bandwidth of the channel rapidly fluctuates over time.
Furthermore, in a wireless environment, the amount of bandwidth available to the system is fixed and scarce. Adding bandwidth to the radio link may be expensive or even impossible due to regulatory constraints.
In addition, the issues in connection with increasing the transmission bandwidth are substantially different in the wireless environment. In a wired environment increasing the throughput is simply a matter of allocating as much bandwidth as possible to the connection. In a wireless environment, part of the bandwidth is used in error correction. More error correction means less payload. However, more error correction increases the probability of correct delivery without retransmissions. Thus, in the wireless environment increasing the end-to-end throughput may be obtained by reducing bandwidth assigned to payload and using the freed bandwidth for error correction.
The Data Link Control (DLC) protocols available to date do not attempt to be inclusive as complete DLC protocols. Basically, off-the-shelf protocols intended for different media have been adopted for wireless systems. Even though some of those protocols are standardized, they are not very efficient for the wireless system. Also, some of the interactions between the non-wireless protocols and the communication system have caused a lot of complexities. For example, a point to point protocol (PPP) is currently used to conduct part of the functionality needed for the DLC layer. However, such a protocol imposes new limitations over the communication system. Moreover, for the DLC protocol to support the IP quality of service (QoS), the PPP encapsulation must be undone which lowers the throughput.
Also, the Layer-2 ARQ protocol as defined in the current CDMA standard xe2x80x9cData Service Option Standard for Spread Spectrum Digital Cellular Systemsxe2x80x9d, Ballot version, November 1998 (TIA/EIA/IS-707A), is a RLP which consists only of a Selective-Repeat (SR) scheme. TIA/EIA/IS-707A RLP uses the SR scheme for all classes of traffic. The latency introduced by the initialization procedures of this protocol is unnecessary and inefficient for traffic profile with short and infrequent data bursts. Furthermore, the existent RLP protocol is a xe2x80x9cbest effortxe2x80x9d type protocol, which tries to retransmit the frames received in error for a number of times and then gives up after a certain number of attempts.
Accordingly, there is a need for a specialized DLC protocol for the 3G wireless systems which can satisfy the demand for advanced multimedia services to support multiple concurrent voice, packet data, and circuit data services, each having various QoS requirements.
Also, there is a need to improve the existing ARQ protocols to satisfy different QoS requirements.
It is an object of the present invention to provide a Data Link Control(DLC) protocol which supports the Internet Protocol (IP) in a wireless communication system and to alleviate totally or in part the drawbacks of the prior art. This novel DLC removes the need for non-wireless data link protocols with their inherent limitations imposed. Furthermore, the DLC protocol according to the invention is capable of interfacing with the existing non-wireless Data Link Protocols.
It is another object of the present invention to provide a DLC protocol for a wireless communication system, which supports IP Quality of Service (IPQoS) requirements for various advanced multimedia services.
Still another object of the invention is to provide improved multi-mode Layer 2 Automatic Repeat Request (ARQ) protocol for a wireless system.
According to one aspect of the invention a Data Link Control (DLC) protocol for direct support of a network layer protocol is provided. At a transmit end of a wireless communication system, the DLC protocol of the invention uses a plurality of QoS data planes for processing the received data packets according to a particular QoS requirement and to generate radio link protocol data units (RLP PDUS) to be transmitted to a receiving end. According to the information in a received network layer data packet, a QoS processing module converts the received data packets into QoS oriented data packets and redirects the QoS oriented data packets to the appropriate QoS data plane. A new level of error recovery is created at the Link Access Control (LAC) as the RLP PDUs have variable length which is dynamically adjusted in response to the conditions of the communication link. An improved dual mode ARQ is also provided at the Medium Access Control (MAC) for improving the quality of the air transmission especially when the traffic profile of the service includes data bursts with large inter-arrival time.
According to another aspect of the invention, a method for processing network layer protocol data packets for transmission over a wireless communication system is provided. A plurality of QoS data planes are created at the Data Link Layer level of the wireless communication system for processing the data packets received from the network layers according to a Class of Service (CoS), and to generate RLP PDUs to be transmitted over the Physical Layer. The method comprises the steps of converting the received network layer protocol data packets into QoS oriented data packets according to the information contained in the received data packets; directing the QoS oriented data packets to an appropriate QoS data plane, each QoS data plane having its dedicated LAC and MAC instances; at the LAC level, dividing the QoS oriented data packets in smaller size sequence frames and encapsulating a plurality of sequence frames to form HDLC-like LAC frames; at the MAC level, receiving the LAC frames and regulating their delivery to the radio link protocols (RLPs) and converting the LAC frames into protocol data units (RLP PDUs).
Advantageously, the DLC protocol according to the invention, enables direct support of the IP networking and IP Quality of Service (IP QoS)in the wireless system by introducing QoS data planes to handle different Classes of Service (CoS) defined at the DLC layer. It also introduces a new level of error recovery, i.e. an Automatic Repeat Request (ARQ) at the Link Access Control (LAC) sublayer to insure better connectivity and prevent propagation of errors to higher layers. This functionality enables less delays and better flow control.
The DLC protocol according to the present invention removes the need for other non-wireless data link protocols, such as PPP, to connect to the IP. In addition, the MAC disclosed in conjunction with the DLC protocol of the invention introduces a multi-mode RLP which supports different QoS requirements, particularly for bursty as well as non-bursty traffic conditions.
Other aspects and features of the present invention will become apparent to those skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.